Primer Data Communication Technology SDH Decnet AppleTalk Novell-IPX MPOA BISYNC/BSC Terminal-Multiplexer ... D.I. Lindner / D.I. Haas Data Communication Primer, v6.4 24 How Long Is

Primer Data Communication Technology

Pillars of Data Communication: Framing, Layering, Protocol, Error Recovery, ARQ

TDM, Circuit Switching, Packet Switching

© 2012/2016, D.I. Lindner / D.I. Haas Data Communication Primer, v6.4 2

Today's Internet Technologies / Terms

IPv6

IP Routing

ISP TCP

HTTP

Ethernet Switching

VOIP IPsec-VPN

MPLS

VLAN RSTP

LACP

SNMP UDP

BGP

IP Address

Address Aggregation

CIDR

NAT

MPLS-VPN

MPLS-TE

L3-QoS (DSCP)

L2-CoS

Autonomous Systems

6rd

HSRP/VRRP/GLBP

DNS

TLS

ADSL/VDSL

RTP

IPv4 ICMP

PIM-SM SRTP

SSL-VPN

Firewall

IDS/IPS

NetFlow WLAN

PPP

Radius

AAA VIX

WWW

HTML Load Balancer

Anycast

DNSSEC

VPLS

Pseudowire LISP

Unicast

IGMP Carrier Ethernet

L2TPv3

DMVPN GetVPN

SMTP FTP POP3

IMAP

SSH ARP

NHRP IP Mobility

IKE

ND

SLAAC

SIP

MLD

NAT64/DNS64

ISATAP

Teredo

6PE 6VPE 6to4

NAT444 DS-Lite

Shim6 HIP

Multicast NAC

Virtualization

Cloud

Data Center LTE

VM

Trill

OTV

MIME

SSM

EIRGP IS-IS

OSPF RSVP PPTP

LDAP

NMS

SDN

Openflow

NVF

Segment Routing

MAC Address


Yesterday’s Technologies / Terms

X.25

ISDN

Frame-Relay

ATM

HDLC

PNNI

CNLP

OSI

Token-Ring SNA APPN

Token-Bus DQDB

FDDI

Source-Route Bridging

SR Translational Bridging LANE

NHRP (ATM)

L3-QoS (RSVP)

PDH SDH

Decnet AppleTalk

Novell-IPX

MPOA BISYNC/BSC

Terminal-Multiplexer MARS, MCS

Transdata

Datex-P Datex-L

B-ISDN

FTAM

X.500 DAP JTM

LAPB LAPF

BUS/LES

MAN MAP

MHS PABX

PAD

PSTN SDLC

SONET

VGAnyLan

ATMR LAPD LAPM VT

SMDS

ATOM

RIP

CSMA/CD


Confused ?

Destroyed ?

Frustrated ?

!!! Take the Data Communication Lectures !!!

https://www.ict.tuwien.ac.at/lva/384.081/index.html


Generic Pillars of Data Communication –  Serial Transmission Technology

•  Bit Synchronization •  Encoding / Decoding

–  Framing and Error Detection •  Frame Synchronization, Checksum

–  Layering, Protocols, Services •  Encapsulation / Decapsulation •  Connectionless versus Connection-oriented •  OSI-7 Layer Model

–  Error Recovery •  ARQ Techniques, Sequence Numbers, Windowing •  Delay-Bandwidth Product

–  Flow Control •  End System to End System •  End System to Network

–  Time Division Multiplexing (TDM) •  Synchronous TDM •  Asynchronous (Statistical) TDM

–  Network Methods •  Circuit Switching •  Packet Switching


Today’s Most Important Technologies –  LAN Technology

•  Ethernet, Ethernet Switching •  Rapid Spanning-Tree, VLAN, LACP •  WLAN (***)

–  IP Network Technology •  IP Unicast Forwarding (Addressing, ARP, ICMP, PPP, HSRP) •  IP Routing (RIP, OSPF) •  Internet Routing, BGP (*), CIDR

–  IP End-to-End Transport •  TCP and UDP

–  IP Administration, Standard Applications, Special Topics •  NAT •  BootP, DHCP, TFTP •  DNS •  FTP, Telnet / SSH •  HTTP, WWW •  VOIP (*) •  Firewall (*), (***)

–  IP Backbone Technology and VPN •  MPLS •  MPLS, MPLS-VPN •  IPsec and IPsec VPNs (*)

–  IP Advanced Topics •  IPv4 Multicast (IGMP, PIM-DM, PIM-SM, SSM) (*) •  IPv6 (“The New IP”) •  LISP (Locator / Identifier Separation Protocol) (**)

–  Virtualization, SDN (Software Defined Networks), NFV (Network Function Virtualization),


Agenda •  Physical Aspects

–  Serialization, Coding –  Framing, Delay Types

•  Protocol Basics –  Layering / CL versus CO –  Error Recovery / Automatic Repeat Request (ARQ) –  Windowing, Delay-Bandwidth Product, Flow Control

•  TDM Basics –  Synchronous TDM –  Asynchronous TDM

•  Network Basics –  Circuit Switching –  Packet Switching

•  Datagram Service / Connectionless Service •  Virtual Call Service / Connection-Oriented Service

–  Summary •  OSI Model – DoD Model


Representation of Symbols for Information Processing, Storage and Exchange •  In the context of computer systems and data

communication •  Discrete levels = "Digital"

–  Resistant against noise

•  How many levels? –  Binary (easiest)

•  Bit (binary digit), values 0 and 1

–  M-ary: More information per time unit!

Binary M-ary (here 4 levels, e. g. ISDN)


1 0 1 1 0 0 1

Source

1

0

1

1

2

n

signal reference

. . . Destination

1

2

n

. . . Bus

Source

1

Destination

1

time

1-bit

clk clk sampling pulse

Transmission of Information: Parallel versus Serial

signal reference

signal reference signal reference


1 0 1 1 0 0 1

Source

ref.

Destination

ref.

time

1-bit

Bit (Clock) Synchronization Receiver Side

Transmitter Clock

Clock Recovery

Circuit

Data tmt TxD Data rcv RxD

sampling pulses


Line Coding Examples

1 0 1 0 1 1 0 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 NRZ

RZ

Manchester

Differential Manchester

NRZI

AMI

HDB3

Code Violation


That Happens To A Signal !!!

Transmitted Signal

Attenuation

Limited Bandwidth Fc

Delay Distortion

Line Noise

Received Signal

0 1 0 0 1 0

0 1 0 1 1 0 Bit Error

Sampling Impulse

time


Requirements & Facts Serial Transmission System •  Information between systems is exchanged in

blocks of bits –  Every block is carried in as so called transmission frames

•  The recognition of the beginning and the end of a block in the received bit stream is necessary –  Frame synchronization

•  Errors on physical lines may lead to damage of digital information –  0 becomes 1 and vice versa –  The longer the block the higher the probability for an error

• Methods necessary for error checking –  Frame protection –  Error detection and recovery



–  Serialization, Coding –  Framing, Delay Types

•  Protocol Basics –  Layering / CL versus CO –  Error Recovery / Automatic Repeat Request (ARQ) –  Windowing, Delay Bandwidth Product, Flow Control






SYNC - Sync Pattern ED - Ending Delimiter SD - Starting Delimiter FCS - Frame Check Sequence

payload

frame header bit

synchronization

control information (protocol header)

checksum frame synchronization

Generic Frame Format

frame trailer

DATA Control FCS ED SD Preamble / SYNC


Preamble

DATA Control FCS ED SD Preamble / SYNC

•  Preamble / SYNC is a special bit pattern –  Used for bit synchronization after an idle period (Preamble) –  Can be used as fill pattern during idle times to keep the

receiver clock synchronized (SYNC) •  Enables PLL synchronization

–  Typically a 0101010...-pattern –  Example: 8 Byte preamble in Ethernet frames


Control Field

•  Is used for implementing protocol procedures •  Contains information such as

–  Frame type, protocol type •  Data, Ack, Nack, Connect, Disconnect, Reset, etc. •  IP, IPX, AppleTalk, etc.

–  Sequence numbers for identification of frame sequence •  Necessary for error recovery and flow control with connection

oriented services

–  Address information of source and destination in case of a multipoint line

–  Frame length, etc.

DATA Control ED SD SYNC FCS


Frame Synchronization

DATA Control FCS ED SD Preamble

•  Beginning and ending of a frame is indicated by SD and ED symbols –  Bit-patterns or code-violations –  Length-field can replace ED (802.3) –  Idle-line can replace ED (Ethernet)

•  Also called "Framing"

Starting Delimiter

Ending Delimiter


Error Control

•  Focus on error detection –  Include enough redundant information with each block of

date to enable receiver to detect only errors occurred -> error detecting codes -> Frame Check Sequence

–  After error detection a retransmission of frame is initiated through protocol feedback to the sender

•  Area of ARQ-techniques •  Feedback Error Control

DATA Control ED SD SYNC FCS

Protected


Frame Protection

•  A frame check sequence (FCS) protects the integrity of our frame –  From Sunspots, Mobile-Phones, Noise, Heisenberg and others

•  FCS is calculated upon data bits –  Different methods based on mathematical efforts: Parity, Checksum,

CRC

•  Receiver compares its own calculation with FCS

DATA Control ED SD Preamble FCS

Protected


Error Control

•  Focus on error correction –  Include enough redundant information with to enable

receiver to correct errors occurred -> error correcting codes ECC (important -> “Hamming Distance”)

–  Forward Error Control (FEC) –  Required for "extreme" conditions

•  High BER (Bit Error Rate), EMR •  Long delays, space links

–  Examples: Reed-Solomon codes, Hamming-codes

DATA Control ED SD SYNC

Protected by encoding using ECC codewords


Time to Transmit A Given Number Of Bytes

Bitrate 9,6 kbit/s 48 kbit/s 128 kbit/s 2,048 Mbit/s 10 Mbit/s 100 Mbit/s 155 Mbit/s 622 Mbit/s 1 Gigabit/s

Number of Byte

Delay inmsec (10-3)

Delay inmsec (10-3)

Delay inmsec (10-3)

Delay inmsec (10-3)

Delay inmsec (10-

3)

Delay inmsec (10-3)

Delay inmsec (10-3)

Delay inmsec (10-3)

Delay inmsec (10-3)

Bit 0,125 0,104167 0,020833 0,007813 0,000488 0,000100 0,000010 0,000006 0,000002 0,000001Byte 1 0,833333 0,166667 0,062500 0,003906 0,000800 0,000080 0,000052 0,000013 0,000008PCM-30 32 26,666667 5,333333 2,000000 0,125000 0,025600 0,002560 0,001652 0,000412 0,000256ATM cell 53 44,166667 8,833333 3,312500 0,207031 0,042400 0,004240 0,002735 0,000682 0,000424Ethernet 64 53,333333 10,666667 4,000000 0,250000 0,051200 0,005120 0,003303 0,000823 0,000512X.25 256 213,333333 42,666667 16,000000 1,000000 0,204800 0,020480 0,013213 0,003293 0,002048IP 576 480,000000 96,000000 36,000000 2,250000 0,460800 0,046080 0,029729 0,007408 0,004608Ethernet 1.518 1.265,000000 253,000000 94,875000 5,929688 1,214400 0,121440 0,078348 0,019524 0,012144FR 8.192 6.826,666667 1.365,333333 512,000000 32,000000 6,553600 0,655360 0,422813 0,105363 0,065536TCP 65.534 54.611,666667 10.922,333333 4.095,875000 255,992188 52,427200 5,242720 3,382400 0,842881 0,524272

1kbit/s = 1000 bit/s !!! 1KByte = 1024 Byte !!!

Serialization Delay (in ms) = [ ( Number of Bytes * 8 ) / ( Bitrate in sec ) ] * 1000


Propagation (Signal) Delay

Tp = Propagation Delay (in ms) = [ ( Distance in m ) / ( velocity in m/sec ) ] * 1000

Total Delay (for a block of bits) = Propagation Delay + Serialization Delay + (Switching Delay)

Distance Delay inmsec (10-3)

Delay inmsec (10-3)

CPU Bus 10 cm 0,0000005 0,00000031 m 0,0000050 0,0000033

RS232, V24/V.28 15 m 0,0000750 0,0000500LAN, Copper, RJ45 100 m 0,0005000 0,0003333LAN, FO, X.21/V.11-V.10 1 km 0,0050000 0,0033333Local Subscriber Line 2,5 km 0,0125000 0,0083333WAN Link Repeater 10 km 0,0500000 0,0333333WAN Link Repeater 100 km 0,5000000 0,3333333WAN FO Link Repeater 1.000 km 5,0000000 3,3333333WAN FO Link Repeater 10.000 km 50,0000000 33,3333333Satellite Link 40.000 km 200,0000000 133,3333333Satellite Link 50.000 km 250,0000000 166,6666667

100.000 km 500,0000000 333,3333333300.000 km 1500,0000000 1000,0000000

v=200.000km/s v=300.000km/s


How Long Is A Bit?

Bitrate Bit Length in meter Bit Length in meter

Analogue Modem 9,6 kbit/s 20833,33 31250,00Analogue Modem 48 kbit/s 4166,67 6250,00DS0 64 kbit/s 3125,00 4687,50ISDN (2B) 128 kbit/s 1562,50 2343,75PCM-30, E1 2,048 Mbit/s 97,66 146,48Token Ring 4 4 Mbit/s 50,00 75,00Ethernet 10 Mbit/s 20,00 30,00Token Ring16 16 Mbit/s 12,50 18,75Fast Ethernet, FDDI 100 Mbit/s 2,00 3,00ATM STM1, OC-3 155 Mbit/s 1,29 1,94ATM STM4, OC-12 622 Mbit/s 0,32 0,48Gigabit Ethernet 1 Gigabit/s 0,20 0,30OC-48 2,5 Gigabit/s 0,08 0,1210 Gigabit Ethernet 10 Gigabit/s 0,02 0,03

Copper LWL - Free Space200.000 km /sec 300.000 km / sec

Length (in m) = [ ( 1 / ( bitrate per sec) ] * [ ( velocity in m/sec ) ]


Propagation Delay And Number Of Bits On A Given Link

Source

0,005 bits

50 bits

Destination

1 kbit/s

10 Mbit/s

1 km

Tp = 0,005ms

Source

1 bit

10.000 bits

Destination

1 kbit/s

10 Mbit/s

200 km

Tp = 1ms

Source

167 bits

1.670.000 bits

Destination

1 kbit/s

10 Mbit/s

50000 km

Tp = 167ms



–  Serial Transmission, Coding –  Framing, Delay Types







Three Important Principles for Data Communication •  Layering

–  Structuring the complex task of data communication into smaller pieces by usage of “layers”

•  Services –  Are provided by a layer to the upper layer and describe

what is exchanged between layers within a system •  Implementation-specific •  World of industry standards created by vendors

•  Protocols –  Are used for communication between the systems (peers)

within a layer •  World of communication standards (IEEE, ITU, IETF, ETSI, OSI)


application software

communication software

communication hardware

OS




OS

Tmt_A Rcv_B

Rcv_A Tmt_B

signal reference

line protocol

Computer A Computer B

Point-to-Point Communication 3 Layer Model

logical relationship between peers

physical wires for transmit and receive


Best-Effort Service: Connection-less Protocol

time time

Datagram's

Station A Station B

transmission of data

Datagram's

like packet or telegram service of a legacy PTT

no error recovery of corrupted frames


Reliable Service: Connection-oriented Protocol

time time

Connection Request

Connection Acknowledgement

DATA

Disconnection Request

Disconnected Acknowledgment

Station A Station B

connection establishment

transmission of data

clearing of connection

like Telco telephone call

error recovery of corrupted frames is possible by usage of ARQ techniques


Connection-oriented Protocols

•  Different definitions –  Some say "protocols without addressing information" and

think of circuit-switched technologies –  Some say "protocols that do error recovery"

–  Correct: "protocols that require a connection establishment before sending data and a disconnection procedure when finished"










ARQ Techniques Overview

•  ARQ protocols guarantee correct delivery of data –  Error recovery by usage of feedback error control –  Retransmission of data (information) frames after errors

are detected by the receiver •  Basic Method:

–  Receiver acknowledges correct receipt of data frame by sending special control frames (ACK) in opposite direction

–  Acknowledgements refer to identifiers (sequence numbers) carried in the protocol header of the original data frame (I)





OS




OS

Tmt_A Rcv_B

Rcv_A Tmt_B

signal reference


Com-SW Layer Implementation Necessary Resource Elements

Protocol State Machine Retransmission List Receive List Timers Control Variables Queues / Mailboxes for operating API





OS




OS

Tmt_A Rcv_B

Rcv_A Tmt_B

signal reference

line protocol


Com-SW Layer Implementation Necessary Protocol Elements

Frame (Control Field)Types: Connect request / ack Disconnect request / ack I, ACK, NACK, SREJ Identifiers


payload

frame header

control information = line protocol header Frame Type Field: Connect Request, I, ACK, NACK, … Identifier Field: N, N+1, …

checksum

Remember Control Field (Generic Frame Format)

frame trailer

DATA Control FCS ED SD SYNC


Idle-RQ versus Continuous-RQ

Data and Acks are sent continuously !!

Idle-RQ Continuous-RQ

half duplex protocol

full duplex protocol


Why Identifiers or Sequence Numbers?

Sender Receiver Data "ABCD"

Ack

Ack

Ack

Data "ABCD"

Data "EFGH"

No Ack? Retransmission!

ABCD

ABCD ABCD

ABCD ABCD EFGH


Modulo 2 Numbering for Identifiers Sequence Numbers 0 and 1

Sender Receiver Data "ABCD" S=0

Ack=0

Ack=0

Ack=1

Data "ABCD" S=0

Data "EFGH" S=1

No Ack? Retransmission!

ABCD

ABCD

ABCD EFGH


Slow !

Vienna Tokyo

"Stop and Wait": Data is traveling round the earth while sender waits for the acknowledgement. In the meantime no data can be sent !!


Nearly Empty Pipe !

Vienna Tokyo

t = 0 s

t = 350 ms

1.5 Mbit/s

This pipe allows 1.5 Mbit/s × 350 ms

= 525,000 bit ≅ 64 KB of data to be stored.

But stop-and-wait only allows one frame to be

outstanding !!!

Assume MTU=1 KByte, then the max rate is (1024 × 8) bit / 0.35 s

≅ 23 Kbit/s


Why we need a Retransmission Buffer?

Vienna Tokyo

Four packets are sent, but due to a network failure none of them arrive (or equivalently they do arrive but all the Acks are lost)

Timeouts !!!

0

0 1

0 1 2

0 1 2 3

.

.

.

.

0 1 2 3

0 1 2 3

0 1 2 3

0 1 2 3

Retransmissions

0

1 0


Full Pipe !

Vienna Tokyo

t = 0 s

t = 350 ms

1.5 Mbit/s

This situation corresponds with a

sliding window


ARQ (Automatic Repeat Requests) Variants

Idle-RQ Selective ACK (SACK)

e.g.TCP modern variant GoBackN

e.g. HDLC, LAPB Positive ACK

e.g. TCP base variant Selective Reject (SREJ)

e.g. HDLC variant

Continuous-RQ Used by TFTP

(Trivial File Transfer Protocol) Based on UDP (User Datagram Protocol)

Note: FTP (File Transfer Protocol)

Based on TCP (Transmission Control Protocol)


Selective Acknowledgement (1) Vienna Tokyo

Data S=0

Data S=1 Ack=0

Ack=2

Ack=3

Data S=2

Data S=3

Data S=1

Ack=1

0

0 1

1 2

1 2 3

Timeout for S=1 1st retransmission

1

1 3

1

0

2 0

3 2 0

1 3 2 0 Reordering necessary

Retransmission Buffer Receive Buffer


Selective Acknowledgement (2)

Vienna Tokyo Data S=0

Data S=1 Ack=0

Ack=2

Ack=3

Data S=2

Data S=3

Data S=1

Ack=1

0

0 1

1 2

1 2 3

Timeout for S=1 1st retransmission

1

1 3

1

0

2 1 0

3 2 1 0

3 2 1 0 Duplicate !!!

Ack=1 1


GoBackN with Sequence Numbers

Vienna Tokyo 0 Data S=0

Data S=1 Ack=1

Data S=2

NACK = 1

0 1

1 2

1 2 3

0

0

0

Data S=1 1 0

2 1 0

Data S=2 Ack=2

Ack=4

1 2 3

2 3

1 2 3 Data S=3 0

Data S=3 3 2 1 0 Sequence

maintained !


Positive ACK with Sequence Numbers

Vienna Tokyo 0 Data S=0

Data S=1 Ack=1

Data S=2

0 1

1 2

0

0

2 0 Data S=3 3 2 0

1 2 3

Timeout S=1

1 2 3 Data S=1 1 3 2 0 Ack=4

Cumulative Ack










Timers - Retransmission Timeout

•  The value for retransmission timeouts for line protocols can be easily calculated using the following parameters –  Bitrate –  Maximum data frame size –  Worst case time at receiver to generate an

acknowledgment –  Size of acknowledgment frame

•  Calculation for network protocols with varying transmission delays is more complex –  Adaptive process is necessary


Send Window and Sliding Window

•  Continuous-RQ techniques would require infinite sender/receiver buffer size (also infinite number of identifiers) –  If we do not restrict the number of unacknowledged

frames •  Send Window W

–  Is the maximum allowed number of unacknowledged frames in the retransmission list

•  Necessary sender-buffer size is W * maximum frame size –  Also called the Window Size

•  Handling procedure –  Is called (Sliding) Windowing


Sliding Window Basics (1)

1 2 3 4 5 6 7 8 9 10 11 12

Window W = 5

Sent but not yet acknowledged

Can be sent as soon as

possible

Can't be send until window moves

....

Usable window time

Event t0:



1 2 3 4 5 6 7 8 9 10 11 12

Window W = 5

Sent and already acknowledged


Will send as soon as possible

can't send until window moves

....

Usable window time

Event t1:



1 2 3 4 5 6 7 8 9 10 11 12

Window W = 5

....

Usable window

time


can't send until window

moves

Event t2:


Windowing with Numbering Modulo W+1

1 2 3 4 5 0 1 2 3 4 5 0

Window W = 5



Will send as soon as possible

can't send until window moves

....

Usable window time

GoBackN and send-window W means W+1 Identifier and numbering with modulo W+1


How Large should be the Window Size?

• Window size depends on –  Bandwidth (bit rate) of the communication channel –  Round-Trip-Time (RTT)

•  = 2 x (propagation + serialization) delay plus response delay of partner

–  (Available buffer size transmitter/receiver)

•  The optimum window size –  must be big enough so that the sender can fully utilize the

channel volume which is given by the Bandwidth-Delay Product –  Window size in Bytes >= BW × RTT –  If smaller: jumping window –  Extreme case: Idle-RQ with W=1


Vienna Tokyo

t = 0 s

t = 350 ms

1.5 Mbit/s

This situation corresponds with a true sliding window

Full Pipe with Continuous-RQ and W = 64


= 525,000 bit ≅ 64 KB of data.

Continuous-RQ (C-RQ) allows several frames to be outstanding. With 1 KByte maximum Frame Size optimum would be W = 64 !!!

W = 64


Nearly Empty Pipe with Idle-RQ and W = 1

Vienna Tokyo

t = 0 s

t = 350 ms

1.5 Mbit/s

This pipe allows storing of 1.5 Mbit/s × 350 ms = 525,000 bit ≅ 64 KB

of data.

Assume 1 KByte (1024 byte) maximum frame size, then the maximal achievable rate is (1024 × 8) bit / 0.35 s ≅ 23 kbit/s

Idle-RQ only allows one frame to be outstanding. That means W = 1 !!!

W = 1


Vienna Tokyo

t = 0 s

t = 350 ms

1.5 Mbit/s

This situation corresponds with a

true jumping window

Only Half Pipe Used with C-RQ and W = 32


= 525,000 bit ≅ 64 KB of data.

With 1 KByte maximum Frame Size and W = 32 the pipe could be used only half the time !!!

W = 32


Jumping Window

Vienna Tokyo





OS




OS

Tmt_A Rcv_B

Rcv_A Tmt_B

signal reference

flow control indicating congestion

Host A Host B

Flow Control


Flow Control: Adaptive Windowing

• Window size could be –  Constant or dynamic during lifetime of a connection

•  Constant window size is used e.g. by HDLC, X.25

•  If window size is dynamic –  A start value is negotiated during connection

establishment –  Actual window size will be dynamically adjusted to an

optimal value •  Receiver continuously advertises optimal value (e.g. based

on availability of free buffer memory) •  Advertised window size = 0 -> STOP •  Advertised window size > 0 -> GO

–  Adaptive windowing (e.g used by TCP)










Introduction

•  Line protocol techniques –  Were developed for communication between two devices over one

physical point-to-point link –  Bandwidth of physical link is exclusively used by the two stations

•  In case multiple communication channels are necessary between two locations –  Multiple physical point-to-point links are needed –  Every point-to-point link is operated by line protocol techniques –  SDM (Space Division Multiplexing) –  Expensive solution

•  One method to use one physical link for multiple channels is –  TDM (Time Division Multiplexing) –  Note: FDM, DWDM, CDM are other methods


TDM versus SDM

00110011001101000111100010010000101001010010101001110100010011001

10011100010101001010101010011110001010001101011011100010101001011

11000111000111100000000000000000000000000000000000000001000000000

101010010111

User A

User B

User C

User D

0011100001101 1011100100100 1000011101101

SDM

User A

User B

User C

User D

1011100111 1011100111 1011100111 1011100111 1011100111

Framed Mode Save wires

User a

User b

User c

User d

User a

User b

User c

User d TDM


TDM Multiplexing / Demultiplexing

•  TDM multiplexer –  Take a number of input channels and - by interleaving them - output

them as one data stream on one physical trunk line –  Demultiplexer does the opposite

A1

B1

C1

D1

A2

B2

C2

D2

Mux

DeMux Trunk Line

Ports Ports

Direction of Transmission

P1 P2

P3 P4

P1 P2

P3

P4

T T


Types of TDM

•  Depending on timing behavior two basic TDM methods –  Synchronous (deterministic) TDM

•  Timeslots have constant length (capacity) and can be used in a synchronous, periodical manner

•  Examples: PDH (E1, T1), SDH (STM-1, STM-4)

–  Asynchronous (statistical) TDM •  Timeslots have variable length and are used on demand

(depending on the statistics of the individual channel communication)

•  Examples: Ethernet, WLAN









Synchronous TDM (1)

C A

User A2

User B2

User C2

User D2

A B C D

User A1

User B1

User C1

User D1

A B C D A B C D D

A

B

C

D

A

B

C

D

Flag

Timeslot

Frame

Trunk- Link

De-Mux Mux

Access-Links User Ports

Periodic frames consisting of a constant number of timeslots Every channel occupies a dedicated timeslot Implicit addressing given by the position of a timeslot in the frame Trunk rate = number of timeslots x access-link rate Each channel experiences constant delay and no delay variation (jitter)

4 × 64 kbit/s + F ≅ 256 kbit/s

64 kbit/s

64 kbit/s

64 kbit/s

64 kbit/s

Direction of transmission

© 2012/2016, D.I. Lindner / D.I. Haas 69 Data Communication Primer, v6.4

Synchronous TDM (2)

C A

User A2

User B2

User C2

User D2

A C D

User A1

User B1

User C1

User D1

A C D A C D D

A

C

D

A

C

D

Trunk- Link

De-Mux Mux

Access-Links User Ports

Timeslot can be used for any kind of communication -> protocol transparency But empty timeslots are not useable by other communication channels -> waste of bandwidth during times of inactivity Lead to development of asynchronous/statistical multiplexing

4 × 64 kbit/s + F ≅ 256 kbit/s

64 kbit/s

64 kbit/s

64 kbit/s

64 kbit/s


Timeslots with Idle Pattern










Asynchronous TDM (1)

Trunk rate is dimensioned for average usage in statistical manner Each user channels can send packets whenever he/she wants Frames have different lengths Buffering is necessary if trunk is already occupied by another channel Explicit addressing by usage of address fields in the frame Not protocol-transparent any more

User A2

User B2

User C2

User D2

User A1

User B1

User C1

User D1

A (A2->A1) B C D (D2->D1)

A

C

D

B

C

D

A C C

D


128 kbit/s

64 kbit/s

64 kbit/s

64 kbit/s

64 kbit/s

Trunk- Link

De-Mux with buffers

Mux with buffers

Access-Links Access-Links

Average data rates ≅ 32 kbit/s Address Fields

Src & Dst

Frame 1 Frame 2


Asynchronous TDM (2)

If other channels are silent, one channel can fully utilize his/her access rate -> better usage of network bandwidth Variable delay and variable delay variation (jitter) Buffer overflow leads to loss of packets


Access-Links Access-Links

User A2

User B2

User C2

User D2

User A1

User B1

User C1

User D1

D (A2->A1) B D (D2->D1) D (D2->D1)

D

A

128 kbit/s

128 kbit/s

128 kbit/s

128 kbit/s

128 kbit/s

Trunk- Link

D











User B

User C

User D

User E

User F

User A

?

How To Connect All Locations?


Networking: Fully Meshed

User A

User B

User C

User D

User F

User E

• Metcalfe's Law: n(n-1)/2 links

•  Good fault tolerance

•  Expensive


Networking: Switching

User A

User B

User C

User D

User F

User E

Network switches could be based on: Synchronous TDM

•  Circuit Switching

or Asynchronous TDM

•  Packet Switching










PA1 PA5

PB1

PB5

PC1 PC5

PD1

PD5

PE1

PE5

PF1 PF5

T1

T2

T2

T3 T3

T4

T4

T1

A

B

C

D

E

F

1

3 4

2

P - access line, T - trunk line

Circuit Switching

TDM-Switch

e.g. E1 f-PDH framing used on all trunk lines T# given us 30 channels a 64kbit/s per trunk line

e.g. 64kbit/s per access port PX#


PA1 -> T2 (1) : A1-B1 PA2 -> T2 (2) : A2-C1 PA3 -> T2 (3) : A3-D1 PA4 -> T1 (1) : A4- F1 PA5 -> T1 (2) : A5-E1

T1 (1) -> PF1 T1 (2) -> PE1

T3 (1) -> PD1 T2 (1) -> PB1 T2 (2) -> PC1 T2 (3) -> T3 (1)

timeslot identifier

PA1 PA5

PB1

PB5

PC1 PC5

PD1

PD5

PE1

PE5

PF1 PF5

A

B

C

D

E

F circuit switching table switch 1

Connections of Device A

T1

T2

T2

T3 T3

T4

T4

T1


1

3 4

2



T1 (1) -> PF1 T1 (2) -> PE1

T3 (1) -> PD1 T2 (1) -> PB1 T2 (2) -> PC1 T2 (3) -> T3 (1)

timeslot identifier

PA1 PA5

PB1

PB5

PC1 PC5

PD1

PD5

PE1

PE5

PF1 PF5

A

B

C

D

E


Connections of Device A Circuit Path PA3 (A) - PD1 (D)

T1

T2

T2

T3 T3

T4

T4

T1


1

3 4

2



T1 (1) -> PF1 T1 (2) -> PE1 T1 (3) -> T4 (1)

T4 (1) -> PD1

PA1 PA5

PB1

PB5

PC1 PC5

PD1

PD5

PE1

PE5

PF1 PF5

A

B

C

D

E


Connections of Device A Circuit Path PA3 (A) - PD1 (D) Restoration

T1

T2

T2

T3 T3

T4

T4

T1


1

3 4

2


TA (1) -> T2 (1) : A1-B1 TA (2) -> T2 (2) : A2-C1 TA (3) -> T2 (3) : A3-D1 TA (4) -> T1 (1) : A4-F1 TA (5) -> T1 (2) : A5-E1

T1 (1) -> TF (1) T1 (2) -> TE (1)

T3 (1) -> TD (1) T2 (1) -> TB (1) T2 (2) -> TC (1) T2 (3) -> T3 (1)

timeslot identifier

TA

TB

TC

TD

TE

TF

A

B

C

D

E

F

TA, TB, ... TF use TDM technique

TDM lines to Devices

switching table switch 1

T1

T2

T2

T3 T3

T4

T4

T1

1

3 4

2


Circuit Switching – Facts

•  Based on synchronous (deterministic) TDM –  Minimal and constant delay –  Protocol transparent –  High bit rate on trunk lines

•  Sum of access links traversing a given trunk –  Possibly bad utilization

•  Idle pattern in timeslots if no data present –  Good for isochronous traffic (voice)

•  Switching table entries –  Static (manually configured) –  Dynamic (signaling protocol) –  Scales with number of connections!


Circuit Switching Data Networks

•  Network providers offer permanent circuit services –  With permanent entries in circuit switching tables –  Optional with fast automatic switchover (50ms) in case of trunk failure –  Leased line

•  Network providers offer switched circuit services –  With dynamic entries in circuit switching tables generated on demand –  Today implementations are based on ISDN only –  Integrated Services Digital Network –  Outband signaling (via D-channel) between ISDN end system (ISDN-

TE) and ISDN-LE (Local Exchange) = that is the local TDM switch –  Communication between ISDN-LEs is based on Signaling System 7

(SS7)

•  Base is PDH or SDH transmission infrastructure


ISDN User-to-Network Interface (UNI)

ISDN-TE

ISDN Network Service

physical access link (I.430, I.431)

ISDN-LE

channel for user data (B-channel)

channel for signaling (D-channel)

(Q.921, Q.931)

…

logical channels multiplexed on physical channel

TE … Terminal Equipment (ISDN end system) LE … Local Exchange (ISDN switch)


Call Setup on D channel via Q.931

Data or Voice Transfer on B channel

Call Release on D channel via Q.931

Usage D-Channel vs. Bearer Channel

ISDN-TE Local ISDN-LE

ISDN-TE

Remote ISDN-TE

ISDN-TE Local ISDN-LE


Basic Rate Interface (BRI)

–  2 B (bearer) channels with 64 kbit/s each •  carrying digitized voice or data

–  1 D (data) channel with 16 kbit/s •  for outband signaling purposes (e.g. Q.931 protocol)

–  2 B and D are synchronous TDM-multiplexed on physical access line

BRI

2 × B

D

Telco Network

144 kbit/s (plus overhead)

ISDN-TE ISDN-LE

UNI (BRI)


Primary Rate Interface (PRI)

–  30 B (Bearer) channels with 64 kbit/s each (USA 23 B) –  1 D (Data) channel with 64 kbit/s

•  for signaling purposes (e.g. Q.931 protocol)

–  30 B and D are synchronous TDM-multiplexed on one physical access line

30 × B

D

PRI 2.048 Mbit/s (E1 Frames)

ISDN-TE ISDN-LE UNI (BRI)


ISDN Big Picture (AIN, SS7)

STP

STP STP

STP

STP STP

SCP SCP

SP … Signalling Point STP … Signal Transfer Point SCP … Service Control Point CST … Circuit Switching Table TC … Transit Center LE … Local Exchange AIN … Advanced Intelligent Network

CST

CST CST

CST

ISDN-LE

ISDN-LE ISDN-LE

ISDN-LE

ISDN-TC

ISDN-TC

voice trunk (PDH, SDH)

outband signalling path (SS7)

Synchronous TDM Switch

SP

SP

SP

SP

SP

SP










A

D C

B 1

2 3 4

5 6

PA

T1

T1

T1 T2

T4

T2

PD

T3

T1 T2

PC

T3

T4 T2

T1

T2

PB

Packet Switching Topology

Unique Network Address Asynchronous

TDM

Buffers

Common Language

Flow Control

Trunk Lines

Access Line


A

D C

B 1

2 3 4

5 6

Packet Forwarding Principle (Store and Forward)

A B

... Packet payload

A B A B

A B time t0

time t2 time t4

time t6

time t1 forwarding decision

of PS2 time t3

forwarding decision of PS3


of PS4

A B ... Source Address / Destination Address


Packet Forwarding is based on Tables

•  Tables contains –  Information how to reach destinations –  Mapping between destination address or local connection

identifier and outgoing trunk or access port –  “Signposts”

•  Two types of tables –  Depending on the actual implementation of packet

switching technology –  Routing tables –  Switching tables


Routing - Addressing

•  Routing in packet switched networks –  Process of path selection in order to forward a packet to a

given destination –  Selection based on (destination) address

•  Address specifies the location of end system –  Contains topology information –  Address must be unique within the network in order to

enable routing based on signposts •  Protocol using unique and structured addresses

–  Is called routed or routable protocol


Routing Types

•  Static routing –  Routing table entries are static –  Based on preconfigured routing tables –  Configuration done by the network administrator –  Non-responsive to network topology changes

•  Dynamic routing –  Routing table entries are variable (dynamic) –  Changes done by routing protocols

•  Communication protocol used between packet switches to find out the network topology and to calculate the best path to any given destination

–  Responsive to any network topology changes


Routing Table Usage / Type of Service

•  Routing tables are differently used –  Depending on the type of service of the packet switching

network •  Packet switched networks based on

–  Connectionless Service (CL) - Datagram service •  Routing tables are used to forward all kind of packets

–  Connection-oriented Service (CO) – Virtual Call service •  Routing tables are used to forward control packets for connection

establishment •  These control packets generate entries in switching tables •  After connection establishment, only the switching tables are used

to forward data packets


Technology Differences - Summary

•  Datagram Principle –  Global and routable addresses –  Connectionless –  Routing table for forwarding of packets

•  Virtual Call Principle –  Local addresses –  Connection-oriented –  Routing table for setup of connections –  Switching table for forwarding of packets










Datagram Service Principles

•  Connectionless service –  Packets can be sent without establishing a logical

connection between end systems in advance –  Packets have no sequence numbers –  They are called “Datagrams”

•  Every incoming datagram –  Is processed independently regarding to all other

datagrams by the packet switches •  The forwarding decision for incoming packets

–  Depends on the current state of the routing table •  Each packet contains

–  Complete address information (source and destination)


A

D C

B 1

2 3 4

5 6

Packet forwarding (CL) is based on routing tables only (Datagram Service, Best-Effort Service)

B PS3 C PS3 D PS3

to next hop B local C PS5 D PS3

to next hop

B PS4 C PS5 D PS6

to next hop

source address

A B

destination address

... payload

A B A B

A B


A C A B

A C A B

D B A B

D B A B

D B

D B

A C

A C

A

D

B 1

2 3 4

5 6

Datagrams are forwarded completely independent from each other based on current state of routing tables


A C A B

A C A B

D B A B

D B

D B

D B

A C

A

D C

B 1

2 3 4

5 6

Best-Effort Service

Bit-error on trunk line

Buffer overflow in switch 3


Datagram Service Facts (1)

•  Packets may be discarded / dropped by packet switches –  In case of network congestion –  In case of transmission errors

•  Best effort service –  Transport of packets depends on available resources

•  The end systems may take responsibility –  For error recovery (retransmission of dropped or

corrupted packets) –  For sequencing and handling of duplicates

•  Reliable data transport requires good transport layer –  "Dumb network, smart hosts"


A B A B

A B

A B A B

A

D C

B 1

2 3 4

5 6

Rerouting – Sequencing Not Guaranteed !

A B A B

D B

A B D B

D B

D B

Rerouting



•  Rerouting in case of topology changes or load balancing means –  Packets with the same address information can take

different paths to destination –  Packets may arrive out of sequence

•  Sequence not guaranteed –  Rerouting on topology change –  Load sharing on redundant paths –  End stations must care


A

D C

B

2 3

Datagram forwarding needs a kill-mechanism to overcome inconsistent routing tables

A B

... Packet payload

A B

A B

time t1


of PS3

A B ... Source Address / Destination Address

B PS2 C PS5 D PS6

to next hop

B PS3 C PS3 D PS3

to next hop

time t3

t4

t5



•  Connectionless behavior –  Faster delivery of first data

–  No resource reservation is possible •  e.g. bandwidth on trunk line for a certain communication between

end systems •  e.g. buffer memory on packet switches

–  Bad “Quality of Service” (QoS)

–  Flow control between packet-switch and end-system •  Would help in case of congestion if proactively performed •  But lack of trust makes it impossible to implement it



•  Advantages –  Small protocol overhead (easy to implement in end

systems and packet switches) –  Fastest delivery of data between end systems because no

connection must be established in advance •  Disadvantage

–  Delivery of packets is not guaranteed by the network, must be handled by end systems using higher layer protocol

–  Proactive flow control between end-system and packet switch is not possible


Network Technologies based on Datagram Method •  IP

–  Packet is called IP datagram –  End system is called IP host –  Packet switch is called IP router

•  IPX (Novell) •  XNS •  Appletalk •  Decnet Phase IV •  OSI CNLP










Virtual Call Principles

•  Connection-oriented service –  Special control packets (call setup packets) establish a

logical (virtual) point-to-point connection between end systems first

–  We call that connection a Virtual Circuit –  After connection is established

•  Data packets can be transmitted across that virtual circuit •  Typically virtual circuit will be closed after data transfer is finished

•  Different methods are possible –  To establish a virtual call service


14 CR A B

A

E C

B 1

2 3 4

5 6

CR ... Call Request

Packet forwarding (CO) is based on special switching tables but call-setup still uses conventional routing tables (Virtual Call Setup 1)

A :14

from to

from to

from to B PS3 C PS3 E PS3

to next hop

Switching Table of PS 4

unique addresses

local connection identifier

packet type


23 CR A B

A

E C

B 1

2 3 4

5 6

CR ... Call Request

14

Virtual Call Setup 2

A :14 3:23

from to

2 :23

from to from to

B PS4 C PS5 E PS6

to next hop


A

E C

B 1

2 3 4

5 6

CR ... Call Request

14

07 CR A B

23


3:07

from to

A :14 3:23

from to

2 :23 4:07

from to

B local C PS5 E PS3

to next hop


44 CR A B

A

E C

B 1

2 3 4

5 6

CR ... Call Request

14

23

07

Virtual connection A - B: 14-23-07-44


A :14 3:23

from to

3:07 B:44

from to

2 :23 4:07

from to

© 2012/2016, D.I. Lindner / D.I. Haas Data Communication Primer, v6.4 117 CA ... Call Accepted

A B CA 44

A

E C

B 1

2 3 4

5 6

14

23

07


44


A :14 3:23

to from

3:07 B:44

to from

2 :23 4:07

to from

© 2012/2016, D.I. Lindner / D.I. Haas Data Communication Primer, v6.4 118 CA ... Call Accepted

A

E C

B 1

2 3 4

5 6

14

23

07


44 A B CA 14


A :14 3:23

to from

3:07 B:44

to from

2 :23 4:07

to from


A

E C

B 1

2 3 4

5 6

14

23

07


44 D 14

D ... Data Packet … payload

Data Forwarding 1

A :14 3:23

from to

3:07 B:44

from to

2 :23 4:07

from to


A

E C

B 1

2 3 4

5 6

14

23

07


44

D 23


Data Forwarding 2

A :14 3:23

from to

3:07 B:44

from to

2 :23 4:07

from to


A

E C

B 1

2 3 4

5 6

14

23

07


44

D 07


Data Forwarding 3

A :14 3:23

from to

3:07 B:44

from to

2 :23 4:07

from to


A

E C

B 1

2 3 4

5 6

14

23

07


44 D 44


Data Forwarding 4

A :14 3:23

from to

3:07 B:44

from to

2 :23 4:07

from to


A

E C

B 14

14

07

virtual circuit A-B (14-23-07-44) 44

27

23

07

44

virtual circuit A-C (27-14-07-44)

Multiplexing of Virtual Circuits

44

44

14 27


Virtual Call Service Facts (1)

•  The sequence of data packets is guaranteed by the network –  Packets can use the established path only

•  Path selection is done during connection setup –  Afterwards, entries of routing table are not used

•  In case of trunk line or packet switch failure –  Virtual circuits will be closed and must be reestablished

again by end systems using call setup packets –  If there is at least one redundant path, packet switches

can establish a new virtual circuit taking the redundant path


Example

BANG



•  Connection-oriented packet switching –  Allows flow control procedures between end system and

packet switch because of connection-oriented approach •  In connectionless packet switching networks flow control is not

possible or only poorly implemented

–  Flow control procedures can avoid buffer overflow and hence network congestion

–  Allows reservation of resources •  Capacity, buffers, cpu time, etc.

–  Can offer Quality of Service (QoS) –  Call setup can be denied by network if QoS can not be

guaranteed



•  Advantages –  Required resources of packet switches can be reserved

during call setup and hence QoS could be provided –  End system view of the network

•  Reliable point-to-point transport pipe based on network internal error recovery, flow control and sequencing procedures (X.25)

•  Higher protocol layers can rely on network services (X.25)

–  Readiness for receipt is tested in advance •  Call setup of SVC service

•  Disadvantages –  Call setup takes time –  More complex protocols for end systems and packet

switches than datagram service


Virtual Call – Summary (1)

•  Connection establishment –  Through routing process (!) –  Globally unique topology-related addresses necessary –  Creates entries in switching tables –  Can reserve switching resources (QoS)

•  Packet forwarding relies on local identifiers –  Not topology related –  Only unique per port –  Swapping of local identifiers (labels) according to the

switching table


Virtual Call – Summary (2)

•  Connection can be regarded as virtual pipe –  Sequence is guaranteed –  Resources can be guaranteed

•  Virtual call multiplex –  Multiple virtual pipes per switch and interface possible –  Pipes are locally distinguished through connection

identifier •  Network failures disrupt pipe

–  Connection re-establishment necessary –  Datagram networks are more robust


Network Technologies based on Virtual Call Method •  X.25

–  Reliable transport pipe because of protocol inherent error recovery and flow control

–  Local identifier = LCN –  In-band signaling

•  Frame Relay –  Virtual circuit technique but no error recovery –  Congestion indication instead of flow control –  Local identifier = DLCI –  Out-band signaling

•  ATM (Asynchronous Transfer Mode) –  Same as Frame Relay but packets with fixed length –  Hence called cell switching –  Local identifier = VPI/VCI –  Out-band signaling










Summary

•  Only two fundamental network principles –  Circuit switching –  Packet switching –  The first is good for real-time voice (traffic) the latter is

good for data traffic –  But everybody wants to have the best of both worlds

•  Packet switching allows two basic types: –  Datagram (CL) versus Virtual Call (CO) –  Different address types (!) for forwarding decision of data

packet •  Unique routable address (CL) •  Local connection identifier (CO)


Circuit Switching

T1

T2

T3

TA T2

T3

T1

T4 T4

T4 T4 T1 TB

User A2

User B5

TA(1) → T1(4) : A1-C9 TA(2) → T2(7) : A2-B5 TA(3) → T2(6) : A3-D1

. . . . . .

. . . . . . T2(6) → T4(1)

T2(7) → T3(18) . . . . . .

. . . . . . T3(18) → T4(5) T3(19) → T1(1)

. . . . . .

. . . . . . T4(4) → TB(9) T4(5) → TB(5)

. . . . . .

TA(2) → T2(7) : A2-B5 T2(7) → T3(18)

T3(18) → T4(5)

T4(5) → TB(5)


Packet Switching

T1

T2

T3

TA T2

T3

T1

T4 T4

T4 T4 T1 TB

User A2

User B5

Address Information

•  Each switch must analyze address information

•  "Store and Forward“ •  Decision about where to

forward is based on tables

Destination Next Hop A local B R2 C R2

..... .....


IP Datagram Service

User A.2

User B.5

R1 R2

R4

R3

R5

Destination A local B R2 C R2

..... .....

A2 B5

Next Hop

A2 B5

A2 B5

Destination Next Hop A R1 B R4 C R3

..... .....

A2 B

5

Destination Next Hop A R2 B R5 C R2

..... .....

A2 B5

Destination Next Hop A R4 B local C R4

..... ..... IP address (structured address Net-ID:Host-ID)

IP Host IP Router

IP Routing Table of R1

Destination Based Routing


P1

Virtual Call – Call Request (CR)

P1

P2

P3

P0 P0

P1

P2 P0 P0 P2

User A.2

User B.5

PS1 PS2 PS3

PS4 PS5

44 CR B5 A2

Destination Next Hop A local B PS2 C PS2

..... .....

In Out P0:44 P2:10

P2 P0

10 CR B5 A2

Destination Next Hop A PS1 B PS4 C PS3

..... .....

In Out P0:10 P3:02

Destination Next Hop A PS2 B PS5 C PS2

..... .....

02 C

R

B5

A2

In Out P1:02 P2:69

69 CR B5 A2

Destination Next Hop A PS4 B local C PS4

..... .....

In Out P0:69 P2:19

19 CR B5 A2

Routing Table of PS1

Switching Table of PS1


P1

Virtual Call – Call Accepted (CA)

P1

P2

P3

P0 P0

P1

P2 P0 P0 P2

User A.2

User B.5

PS1 PS2 PS3

PS4 PS5

P2 P0 In Out P0:10 P3:02

02 CA

B5

A2

19 CA B5 A2

In Out P0:69 P2:19

In Out P1:02 P2:69

69 CA B5 A2

In Out P0:44 P2:10

10 CA B5 A2 44 CA B5 A2


Virtual Call – Data Transfer

P1 P1

P2

P3

P0 P0

P1

P2 P0 P0 P2

User A.2

User B.5

PS1 PS2 PS3

PS4 PS5

P2 P0 In Out P0:10 P3:02

In Out P0:69 P2:19

In Out P1:02 P2:69

In Out P0:44 P2:10

44 10

02

69 19

Forwarding performed by switching tables


Taxonomy of Network Technologies

Circuit Switching Packet Switching

Dynamic Signalling

Static Configuration Datagram Virtual Call

•  Synchronous (Deterministic) Multiplexing

•  Low latency (constant delay) •  Designed for isochronous

traffic

•  Asynchronous (Statistical) Multiplexing

•  Store and forward (variable delay)

•  Addressing necessary •  Designed for data traffic

ISDN

PDH SONET/SDH

IP IPX AppleTalk

X.25 Frame Relay ATM

Connectionless Connection-oriented Q.931, SS7, ... Manual configuration










Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Link Layer

Physical Layer

Physical Line

real transport peer to peer communication on a logical connection using the layer-specific protocol

The 7 OSI Layers

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Link Layer

Physical Layer

7

6

5

4

3

2

1


Encapsulation and Decapsulation Principle

L7

L4

L3

L2

L1

L5

L6

DATA

DATA

A-PDU

P-PDU

S-PDU

T-PDU

N-PDU

7

4

3

2

1

5

6

DATA

101000111010010110100101001010000100101010001010101010101010010110001001010101010100101111100000101010

L-PDU or "Frame"

N-PDU or "Packet"

T-PDU or "Segment"

S-PDU

P-PDU

A-PDU


Practical Encapsulation

Ethernet Frame

IP Packet

TCP Segment

HTTP Message

HTML Webpage


Application Layer Protocol

Presentation Layer Protocol

Session Layer Protocol

Transport Layer Protocol

7 6 5 4 3 2

3 2

3 2

3 2

3 2

7 6 5 4 3 2

1 1 1 1 1 1

LAN A Intermediate Network LAN B

ES A ES B IS 1 IS 2

OSI Model with Intermediate Systems


ES A ES B

LAN 1 POTS … Plain Old Telephony System

WANs

7 6 5 4 3 2 1

Appl. 7 6 5 4 3 2 1

Appl. PDH ISDN

IS 2 3

2 2 1 1

IS 1 3

2 2 1 1

LAN 2

M M

IS 3 3

2 2 1 1

Example Topology with ES and IS

POTS

LAN 3


Physical Layer (1)

•  Mechanical and electrical specifications

•  Access to physical medium •  Generates bit stream •  Line coding and clocking •  Bit synchronization •  Link management •  Examples

–  LAN: Ethernet-PHY, 802.3-PHY –  WAN: X.21, I.400 (ISDN),

RS-232

Application Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Session Layer

Presentation Layer


7 6 5 4 3 2 1

Appl. 7 6 5 4 3 2 1

Appl.

PDH ISDN

3 2 2 1 1

3 2 2 1 1 M M

3 2 2 1 1

Physical Layer (1)

POTS

Layer 1 Protocol Layer 1 Protocol


Data Link Layer (2)

•  Reliable transmission of frames between two NICs

•  Framing •  Frame Synchronization •  FCS •  Physical Addressing of NICs •  Optional error recovery •  Optional flow control •  Examples:

–  LAN: 802.2 –  PPP, LAPD, LAPB, HDLC

Application Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Session Layer

Presentation Layer


7 6 5 4 3 2 1

Appl. 7 6 5 4 3 2 1

Appl.

PDH ISDN

3 2 2 1 1

3 2 2 1 1 M M

3 2 2 1 1

Data Link Layer (2)

POTS

Data Link 1

Layer 2 Protocol

Data Link 3 Data Link 2


Network Layer (3)

•  Transports packets over packet switching networks –  Routing / Switching

•  Provides structured addresses to name networks –  N-SAP address

•  Fragmentation and reassembling •  Examples:

–  CLNP –  IP, IPX –  Q.931, X.25

Application Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Session Layer

Presentation Layer


7 6 5 4 3 2 1

Appl. 7 6 5 4 3 2 1

Appl.

PDH ISDN

3 2 2 1 1

3 2 2 1 1 M M

3 2 2 1 1

Network Layer (3)

POTS

Layer 3 Protocol

end-to-end connectivity


Transport Layer (4)

•  Transport of segments between applications (end systems) –  Reliable if error recovery by ARQ

•  Application multiplexing through T-SAPs –  Transport Addresses

•  Sequence numbers and Flow control

•  Optional QoS Capabilities •  Examples:

–  TCP (UDP) –  ISO 8073 Transport Protocol

Application Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Session Layer

Presentation Layer


7 6 5 4 3 2 1

Appl. 7 6 5 4 3 2 1

Appl.

PDH ISDN

3 2 2 1 1

3 2 2 1 1 M M

3 2 2 1 1

Transport Layer (4)

POTS

Layer 4 Protocol


4

ES A

4

ES B

Transport Pipe

How Layer 5 sees the Network


Functions of Higher Layers

•  Layer 5 (session layer) –  Coordinates and controls dialogue between

different end systems •  Layer 6 (presentation layer)

–  Responsible for common language between end systems (conversion, adaptation of data)

•  Layer 7 (application layer) –  Supports user with common network applications

(e.g. file transfer, virtual terminal) or basic network procedures in order to implement distributed applications (e.g. transaction systems)


Session Layer (5)

•  Provides a user-oriented connection service –  Synchronization Points

•  Little capabilities, usually not implemented or part of application layer –  Telnet: GA and SYNCH –  FTP: re-get allows to continue an

interrupted download –  ISO 8327 Session Protocol

Application Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Session Layer

Presentation Layer


Presentation Layer (6)

•  Specifies the data representation format for the application

•  Examples: –  MIME (part of L7) and UUENCODING

(part of L7) –  ISO: ASN.1 and BER

Application Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Session Layer

Presentation Layer


Application Layer (7)

•  Provides network-access for applications

•  Examples: –  ISO 8571 FTAM File Transfer Access +

Management, X.400 Electronic Mail, CMIP

–  SMTP, FTP, SNMP, HTTP, Telnet, DNS, …

Application Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Session Layer

Presentation Layer


Padlipsky's Rule

If you know what you're doing, three layers is enough. If

you don't, even seventeen won't help.


DoD 4-Layer Model (Internet)

Transport Layer

Network Layer

Data Link Layer

Process Layer

Transport Layer

Network Layer

Data Link Layer

Process Layer

"Frame"

„Datagram = CL Packet"

„TCP/UDP Segment"


IP transmission over

ATM RFC 1483

IEEE 802.2 RFC 1042

X.25 RFC 1356

FR RFC 1490

PPP RFC 1661

TCP/IP Protocol Suite

Physical

Link

Network

Transport

Session

Presentation

Application SMTP HTTP HTTPS FTP Telnet

SSH DNS DHCP (BootP) TFTP etc.

TCP (Transmission Control Protocol)

UDP (User Datagram

Protocol)

IP (Internet Protocol) ICMP

ARP RARP

Routing Protocols

RIP OSPF BGP

( US-ASCII and MIME )

( RPC )


The Internet perspective is implement it, make it work well, then write it down.

The OSI perspective is to agree on it, write it down, circulate it a lot and now we'll see if

anyone can implement it after it's an international standard and every vendor in the

world is committed to it.

One of those processes is backwards, and I don't think it takes a Lucasian professor of

physics at Oxford to figure out which.

Marshall Rose, "The Pied Piper of OSI"


Layer 1 Devices

•  Adapts to different physical interfaces •  Amplifies and/or refreshes the physical signal •  No intelligence •  Examples: Repeater, Hub, ISDN NT1

Application

Transport Network

Data Link Physical

Session Presentation

Application

Transport Network

Data Link Physical


Repeater


Layer 2 Devices

•  Filter/Forwards frames according Link Layer Address •  Incorporates Layer 1-2 •  LAN-Bridge (“Ethernet Switch")

Application

Transport Network

Data Link Physical


Application

Transport Network

Data Link Physical


Bridge


Layer 3 Devices

•  "Packet Switch" or "Intermediate System" •  Forwards packets to other networks

according structured address •  Terminates Links •  IP Router,

WAN-Switch –  X.25 –  Frame-Relay –  ATM

Application

Transport Network

Data Link Physical


Application

Transport Network

Data Link Physical


Router


A Practical Example

Physical (Twisted Pair)

Physical (Serial Line)

Physical (Wireless)

Link (Ethernet)

Link (HDLC)

Link (WLANI)

Network (IP)

Transport (TCP)

Firefox Browser

Apache Webserver

MAC Address

MAC Address

Simple or dummy Address

What is my destination application?

Where is my destination network?

Just move this frame to the next NIC

Documents

Primer Data Communication Technology SDH Decnet AppleTalk Novell-IPX MPOA BISYNC/BSC Terminal-Multiplexer ... D.I. Lindner / D.I. Haas Data Communication Primer, v6.4 24 How Long Is